Cataract extraction is one of the most commonly performed surgical procedures in the world with estimated 2.5 million cases performed annually in the United States and 9.1 million cases worldwide in 2000. This was expected to increase to approximately 13.3 million estimated global cases in 2006. This market is composed of various segments including intraocular lenses for implantation, viscoelastic polymers to facilitate surgical maneuvers, disposable instrumentation including ultrasonic phacoemulsification tips, tubing, and various knives and forceps. Modem cataract surgery is typically performed using a technique termed phacoemulsification in which an ultrasonic tip with an associated water stream for cooling purposes is used to sculpt the relatively hard nucleus of the lens after performance of an opening in the anterior lens capsule termed anterior capsulotomy or more recently capsulorhexis. Following these steps as well as removal of residual softer lens cortex by aspiration methods without fragmentation, a synthetic foldable intraocular lens (IOL) is inserted into the eye through a small incision.
One of the earliest and most critical steps in the procedure is the performance of capsulorhexis. This step evolved from an earlier technique termed can-opener capsulotomy in which a sharp needle was used to perforate the anterior lens capsule in a circular fashion followed by the removal of a circular fragment of lens capsule typically in the range of 5-8 mm in diameter. This facilitated the next step of nuclear sculpting by phacoemulsification. Due to a variety of complications associated with the initial can-opener technique, attempts were made by leading experts in the field to develop a better technique for removal of the anterior lens capsule preceding the emulsification step. The concept of the capsulorhexis is to provide a smooth continuous circular opening through which not only the phacoemulsification of the nucleus can be performed safely and easily, but also for easy insertion of the intraocular lens. It provides both a clear central access for insertion, a permanent aperture for transmission of the image to the retina by the patient, and also a support of the IOL inside the remaining capsule that would limit the potential for dislocation.
Using the older technique of can-opener capsulotomy, or even with the continuous capsulorhexis, problems may develop related to inability of the surgeon to adequately visualize the capsule due to lack of red reflex, to grasp it with sufficient security, to tear a smooth circular opening of the appropriate size without radial rips and extensions or technical difficulties related to maintenance of the anterior chamber depth after initial opening, small size of the pupil, or the absence of a red reflex due to the lens opacity. Some of the problems with visualization have been minimized through the use of dyes such as methylene blue or indocyanine green. Additional complications arise in patients with weak zonules (typically older patients) and very young children that have very soft and elastic capsules, which are very difficult to mechanically rupture.
Many cataract patients are astigmatic. Astigmatism can occur when the cornea has a different curvature one direction than the other. IOLS are used for correcting astigmatism but require precise placement, orientation, and stability. Complete and long lasting correction using IOLs is difficult. Further, IOLs are not presently used to correct beyond 5D of astigmatism, even though many candidates have more severe aberrations. Correcting it further often involves making the corneal shape more spherical, or at least more radially symmetrical. There have been numerous approaches, including Corneaplasty, Astigmatic Keratotomy (AK), Corneal Relaxing Incisions (CRI), and Limbal Relaxing Incisions (LRI). All are done using manual, mechanical incisions. Presently, astigmatism cannot easily or predictably be fully corrected. About one third of those who have surgery to correct the irregularity find that their eyes regress to a considerable degree and only a small improvement is noted. Another third find that the astigmatism has been significantly reduced but not fully corrected. The remaining third have the most encouraging results with the most or all of the desired correction achieved.
What is needed are ophthalmic methods, techniques and apparatus to advance the standard of care of the astigmatic cataract patient.